Subjective experiences called sensations, described as modalities of biological receptors, have been correlated with the receptors, the afferent axons, and the central connection in the brain that they activate. The central connections, represented by a neuronal circuit, may be viewed as a sensation generating mechanism that generates the sensation defined by the modality of the receptor. The sensation generating circuit, consisting of the afferent axons and the central connections in the brain activated by the receptor, is studied by reverse engineering the “itch-feeling” modality of a mechanoreceptor. The study is performed on a robotic model, called a itch-scratch robotic model, that is designed to reverse engineer the sensorimotor control functions of human “itch-scratch” behavior patterns. The subjective experiences of the robot, viewed as modalities of robotic sensors, may form a basis for a quantitative definition of “consciousness” that consists of modalities described as sensations and emotions.